Wavelength division multiplexed passive optical network (WDM-PON) networks for long reach (100 km) telecommunications access networks have been considered by D. B. Payne and R. P. Davey et al. “The Future of Fibre Access Systems”, BT Technol. J. 20.4, p. 104-114 (2002). WDM-PON networks can also be applied to sensor applications. However to collect data in real-time from many distributed sensors it is necessary to reduce uncertainty in event measurement. It is also desirable to minimise the electrical power consumption of the remote equipment.
There is increasing demand for high-speed readout of large capacity remote sensor systems for applications such as neutrino telescopes. These applications frequently require an optical communications system capable of collecting event data from a remote sensor array comprising many 1000's of detectors and transporting it back to a centralised data acquisition system. Event timing is critical in these applications, hence it is very important that the data collection systems preserves the event timing to a high precision. Currently, these systems tend to use a ‘store-and-forward’ approach where event information is time-stamped relative to a centralised master clock signal, recorded with the detector identity information, buffered, and then multiplexed with other event information for transmission to the data processing centre. A major difficulty with this approach is calibrating the clock distribution system to take account of the different propagation delays between the clock source and the detectors. This leads to a significant amount of remote electronics which must be powered, often in difficult environments (e.g. sub-sea).
This invention, at least in its preferred embodiments, describes an optical communications architecture that is capable of supporting both very large scale detector arrays and preserving timing information with minimal remote electronics.